This invention concerns providing cellular polymers suitable for use in products for absorbing body fluids such as for example, sanitary napkins, catamenial tampons, diapers, bandages, surgical dressings and the like. Such materials, commonly referred to as foams have already been considered for use in such products and in this connection, polyurethane foams, polyester foams and cellulose foams have been suggested.
While these foams, in the main, have been capable of absorbing body fluids to varying degrees, their properties have fallen short of those preferred for products such as diapers, sanitary napkins and the like. One such shortcoming is that while these foams may be formulated to be hydrophilic and hence initially take up large quantities of aqueous liquids, when subjected to pressure such liquid is easily expressed, i.e., the fluid retention properties of these foams are poor. The reason for this is that most of the liquid held by the foam is mechanically held in the cellular void spaces and every deformation caused by external pressure tends to collapse the cell walls, reduce the available void volume and hence express the liquid. Needless to say, such deforming pressure is to be expected in absorbent products worn by the user.
It has been suggested that the fluid retention may be improved by incorporating additional absorbent polymers into the foam. Such additional polymers, commonly called hydrocolloids or superabsorbents are water insoluble, swellable, polyelectrolytes capable of holding many times their weight of liquids and retaining these liquids under pressure. The insoluble polyelectrolytes are blended into the foaming mixture as solid particles during the foaming reaction which forms the foam and hence are distributed in the finished foam matrix. Such a technique is described in U.K. Pat. No. 1,550,614. Unfortunately, it has been found that when the resulting material is wet with body fluids, some of the swollen gel-like superabsorbent is easily, detached from the foam matrix thus reducing its efficiency in retaining liquids within the cells of the foam. Additionally, it has been found that a substantial portion of the superabsorbent is encapsulated in the polymeric foam matrix and hence is inhibited from contact with the liquid and restricted in its abilities to swell and retain liquid.
Accordingly, there is a need for a better way of providing liquid retentive cellular polymeric absorbent materials.